Electric power steering apparatus

Abstract

An electric power steering apparatus has a steering mechanism SM having universal joints 4, 6 in a torque transmitting system, a steering toque detecting unit 14, a steering angle detecting unit 18, a torque fluctuation detecting unit 43 for detecting a torque fluctuation due to the crossing angle α in the universal joints 4, 6 on the basis of the steering angle θ detected by the steering angle detecting unit 18 and any one of the steering torque T detected by the steering torque detecting unit, a current command value It and self-aligning torque SAT; and a current command value correcting unit 44 for correcting the current command value on the basis of the torque fluctuation detected by the torque fluctuation detecting unit 43 and the steering angle θ detected by the steering angle detecting unit 18.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]This invention relates to an electric power steering device designed to assist steering by controlling the drive of a steering assistant motor on the basis of steering torque due to steering of a steering wheel thereby to transmit the rotating force of the motor to a steering mechanism.[0003]2. Description of Related Art[First Problem][0004]In such an electric power steering apparatus which gives the steering assistant force generated by the electric motor to the steering mechanism having the universal joint in the torque transmitting system, a torque fluctuation due to the universal joint is generated. In order to restrict the torque fluctuation, there is a known electric power steering apparatus which acquires a correction coefficient corresponding to the steering angle of a steering shaft, computes a correction motor current command value on the basis of the correction coefficient and a motor current command value de...

AI Technical Summary

Benefits of technology

[0010]In view of the first problem, one object of this invention is to provide an electric power steering apparatus which can detect a torque fluctuation due to changes in a joint angle (crossing angle) and control the motor so as to cancel the torque fluctuation. Another object of this invention is to provide an electric power steering apparatus which can reduce changes in a manual input by steering of a driver even where the thrust becomes insufficient because of the torque fluctuation due to changes in the tilting angle. Still another object of this invention is to provide an electric power steering apparatus which can execute the motor control according to a torque fluctuation so that the thrust exceeding the maximum rack thrust of the electric power steering apparatus is not applied to the rack.

[0011]Further, in view of the second problem, another object of this invention is to make torque control according to a torque fluctuation due to changes in a cardan universal joint angle. Another object of this invention is to reduce changes in a manual input by steering of a driver even where the thrust becomes insufficient because of the torque fluctuation due to changes in the tilting angle. Still another object of this invention is to implement the motor driving according to the torque fluctuation so that the thrust exceeding the maximum rack thrust of the electric power steering apparatus is not applied to the rack.

[0055]In accordance with the first through sixth aspects of this invention, the torque fluctuation due to changes in the tilting angle of the steering shaft is detected on the basis of the steering angle and any one of the steering torque, current command value and self-aligning torque and the current correction value is correspondingly computed. For this reason, without detecting the tilting angle, changes in a manual input by steering of a driver can be reduced.

[0056]Further, the steering assistant force generated in the electric motor can be effectively used to the utmost while surely preventing the thrust exceeding the maximum permissible torque in the electric power steering apparatus from being supplied to the torque transmitting system.

[0057]In accordance with the seventh through twelfth aspects of this invention, the torque control corresponding to a torque fluctuation due to a change in a cardan universal joint angle can be executed. Further, in accordance with this invention, even if a shortage of the thrust is generated by the torque fluctuation due to the change in the tilt angle, a change in the manual input due to steering by the driver can be reduced. Further, in accordance with this invention, it is possible to prevent the thrust exceeding the maximum rack thrust of the electric power steering apparatus from being applied to the rack. In addition, the motor output can be effectively used to the utmost.

Problems solved by technology

So, as the case may be, the prior art cannot cope with changes in the joint angle (crossing angle) by an electric or manual tilting mechanism.

However, if changes in the joint angle (crossing angle) cannot be detected or a necessary rack thrust exceeds the maximum thrust of the motor, because of shortage of thrust, changes in a manual input by steering of the driver occurs.

This problem has not been yet solved.

So, as the case may be, the related art cannot cope with changes in the joint angle (crossing angle) by an electric or manual tilting mechanism.

However, if a necessary rack thrust exceeds the maximum thrust of the motor, because of shortage of thrust, changes in the manual input by steering of the driver occurs.

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